1. Field of the Invention
This invention relates to a coating compositions and coatings containing very small copper tubes which can dispense substances toxic to pests. Particularly this invention relates to coatings containing copper or nickel coated lipid tubule microstructures capable of dispensing antimicrobial, algaicidal, herbicidal, pesticidal and mixtures of these compositions to the environment adjacent the coating.
2. Description of the Prior Art
As man constructs artifacts, nature, in the form of weather, microbes and marine life, works to break the artifact down and return it to nature. Since before recorded history, man has applied coatings to artifacts to both beautify and protect the artifact.
Coatings incorporating materials which are aimed at destroying or diverting microbes and marine life are known. The most common coatings are paints used on land based structures of all types and marine coatings used on seaside and seaborne artifacts such as pilings, ship hulls, towers and other structures.
Biological fouling on artifact surfaces such as ship hulls exposed to seawater is a problem which has existed since man first put to the sea. The diversity of fouling organisms and the environments in which they live create complex problems which any useful antifouling coating must overcome. Because these organisms add weight and hydrodynamic drag when they attach to vessels, effective hull fouling control is necessary to minimize fuel consumption, maintain operational speed and maneuverability, and preserve the hull from corrosion.
The schemes to defeat the attachment of drag producing organisms to ships and other man made artifacts almost matches the diversity of the organisms themselves. Any useful biocidal system must be effective against organisms which range from slime-forming bacteria and algae to shell-forming invertebrates with minimal damage to the remainder of the environment.
By definition, biocidal agents are highly toxic to the target species and to other animals and plants as well. The use of highly toxic and environmentally persistent antifoulants such as lead, mercury, arsenic, and cadmium compounds has been discontinued because of environmental degradation. In addition, the highly effective tributyltin compounds have also been banned from use by several state and federal agencies as well as foreign governments because of the detrimental overall impact.
Although in use in one form or another for over a thousand years, the predominant toxicant in use today is copper in the form of copper sulfate, copper hydroxide, cuprous oxide, copper napthenate or copper metal in powder or sheet form. Too great a concentration of copper can also be harmful to the environment. Paints and coatings in use today contain up to 70% by weight of cuprous oxide and release to the environment far more than the minimum effective amount of copper. Of course, the rate of copper release declines exponentially as the coating ages because exposure of the paint to the environment leaches active toxins until the paint is no longer effective.
Although now the toxin of choice, copper is an environmental hazard which is toxic to invertebrate and vertebrate marine organisms which include many economically valuable species such as oysters and clams, fish and seaweed. The release of copper to the environment must be carefully controlled. In addition, if large quantities are inhaled or ingested during hull repainting, copper oxide can be a hazard for dockyard workers. In contained waters which are frequented by large ocean-going vessels, such as the Suez Canal, the water quality has deteriorated because of high levels of copper. Paints which release high levels of copper may soon be restricted by environmental regulation.
Many inventors have tried to find a way of balancing the beneficial against the detrimental effects of releasing copper or other agents to prevent microbial or marine fouler action adjacent a treated surface. U.S. Pat. No. 4,098,610 describes a biocidal glass additive for marine paints which slowly releases copper. U.S. Pat. No. 4,129,610 describes a water soluble coating for ships which slowly releases copper. Another slow toxin release scheme is described by Foscante et al. in U.S. Pat. No. 4,385,134 where a polymer is used as the slow release agent. Other marine anti-fouling paints and coatings are described in U.S. Pat. Nos. 4,480,011; 4,594,365; 4,602,011. U.S. Pat. No. 4,531,975 describes a marine coating which uses hollow glass bead microspheres or balloons to thicken and change the coating's density.
The mechanisms and history of antifouling paints as well as a discussion of the problems with ablative or erodible type dispensing coating can be found in Foscante et al. U.S. Pat. No. 4,670,481. Foscante describes a paint incorporating tributyltin.
A deficiency in soft ablative paints and in some of the harder leaching paints is rapid mechanical erosion caused by flowing seawater. Often erosion of the coating in the bow, skegs, struts, and keel sections of the ship is more rapid than that in large flat surfaces. Paint is removed quickly from those areas, and the underlying hull is exposed to the ravages of marine fouling agents.
Coatings or paints which incorporate particles of copper or similar materials have the added problem that erosion of the ablative coating surrounding the particle can result in the sudden release of the particle and loss of its benefits. Thus without rational control of the leaching of toxicant from the coating, premature release of large amounts of the biocide in a dropped particle pollutes the environment and reduces the long term performance of marine antifouling paint.
Other problems are present when secondary or auxiliary toxins are used. Secondary toxin materials cannot be effective in promoting extended service lifetimes of conventional coatings unless these highly soluble materials can be protected from rapid leaching and chemical breakdown. Regardless of the myriad schemes developed to release copper and other toxins slowly, the problems of controlled slow release have not been solved.
The need for slow release of biocidal and pesticidal agents is not restricted to a marine environment. In many land environments, mold and other microbial and insect pests attack houses, vehicles and other land based artifacts. Copper and other toxic materials are incorporated into paints coatings and roofing material to suppress or destroy pest activity. U.S. Pat. Nos. 3,894,877; 3,888,683; 3,888,682; and 3,888,176 are all directed at incorporating algaicidal materials into roofing products. Land based artifacts suffer ablative wear similar to sea borne artifacts. A constant exposure of fresh toxic material is needed to protect the coated surface from microbial or pest infestation.
As described in U.S. Pat. No. 3,318,697, it is known to metal coat lipid and wax globules. For pharmaceutical and other purposes, it is known to incorporate materials inside a waxy globule or a liposome. A special kind of liposome form, known as a tubule, was invented at the Naval Research Laboratory. These tubules are hollow tube-shaped microstructures fabricated by self organization of polymerizable diacetylenic phospholipid molecules. Morphologically, tubules are cylinders analogous to soda straws with diameters of approximately 0.5 .mu.m and lengths from 1 to over 200 .mu.m. The preparation of tubules is discussed in an article by Schnur et al. LIPID-BASED TUBULE MICROSTRUCTURES, Thin Solid Films, 152, p. 181-206,(1987) and the articles cited therein. That same article, in which one of the inventors is a co-author, also describes metal coating tubules and using them as "microvials" to "entrap, transport and deliver polymeric reagents to a desired site." see page 200.
Each of the ablative or erodible materials of the prior art tend to dispense particles of material to the environment which causes an uneven and sometimes overly high concentrations of the toxic material. In addition, the agent to be dispensed often reduces or weakens the integrity of the coating. The problems of the ablative coating have not been fully solved.